Metagenomic and Metabolic Profiling of Nonlithifying and Lithifying Stromatolitic Mats of Highborne Cay, The Bahamas

BACKGROUND: Stromatolites are laminated carbonate build-ups formed by the metabolic activity of microbial mats and represent one of the oldest known ecosystems on Earth. In this study, we examined a living stromatolite located within the Exuma Sound, The Bahamas and profiled the metagenome and metabolic potential underlying these complex microbial communities. METHODOLOGY/PRINCIPAL FINDINGS: The metagenomes of the two dominant stromatolitic mat types, a nonlithifying (Type 1) and lithifying (Type 3) microbial mat, were partially sequenced and compared. This deep-sequencing approach was complemented by profiling the substrate utilization patterns of the mats using metabolic microarrays. Taxonomic assessment of the protein-encoding genes confirmed previous SSU rRNA analyses that bacteria dominate the metagenome of both mat types. Eukaryotes comprised less than 13% of the metagenomes and were rich in sequences associated with nematodes and heterotrophic protists. Comparative genomic analyses of the functional genes revealed extensive similarities in most of the subsystems between the nonlithifying and lithifying mat types. The one exception was an increase in the relative abundance of certain genes associated with carbohydrate metabolism in the lithifying Type 3 mats. Specifically, genes associated with the degradation of carbohydrates commonly found in exopolymeric substances, such as hexoses, deoxy- and acidic sugars were found. The genetic differences in carbohydrate metabolisms between the two mat types were confirmed using metabolic microarrays. Lithifying mats had a significant increase in diversity and utilization of carbon, nitrogen, phosphorus and sulfur substrates. CONCLUSION/SIGNIFICANCE: The two stromatolitic mat types retained similar microbial communities, functional diversity and many genetic components within their metagenomes. However, there were major differences detected in the activity and genetic pathways of organic carbon utilization. These differences provide a strong link between the metagenome and the physiology of the mats, as well as new insights into the biological processes associated with carbonate precipitation in modern marine stromatolites

Deep-Sea Nematodes Actively Colonise Sediments, Irrespective of the Presence of a Pulse of Organic Matter: Results from an In-Situ Experiment

A colonisation experiment was performed in situ at 2500 m water depth at the Arctic deep-sea long-term observatory HAUSGARTEN to determine the response of deep-sea nematodes to disturbed, newly available patches, enriched with organic matter. Cylindrical tubes,laterally covered with a 500 µm mesh, were filled with azoic deep-sea sediment and 13C-labelled food sources (diatoms and bacteria). After 10 days of incubation the tubes were analysed for nematode response in terms of colonisation and uptake. Nematodes actively colonised the tubes,however with densities that only accounted for a maximum of 2.13% (51 ind.10 cm−2) of the ambient nematode assemblages. Densities did not differ according to the presence or absence of organic matter, nor according to the type of organic matter added. The fact that the organic matter did not function as an attractant to nematodes was confirmed by the absence of notable 13C assimilation by the colonising nematodes. Overall, colonisationappears to be a process that yields reproducible abundance and diversity patterns, with certain taxa showing more efficiency. Together with the high variability between the colonising nematode assemblages, this lends experimental support to the existence of a spatio-temporal mosaic that emerges from highly localised, partially stochastic community dynamics

Einfluss noradrenerger Stimulation auf die Exzitabilität und funktionelle Konnektivität des somatosensiblen und visuellen Kortex beim Menschen

Noradrenalin spielt eine wichtige Rolle bei der Erregbarkeit von Nervenzellen. Ziel dieser Arbeit war es, den Einfluss des Noradrenalin-Wiederaufnahmehemmers Atomoxetin auf die kortikale Exzitabilität und funktionelle Konnektivität im somatosensiblen und visuellen Kortex zu erforschen. Mittels EEG erfolgte die Ableitung visuell evozierter Potentiale zu unterschiedlichen SOA-(Stimulus onset asynchrony)-Intervallen (107ms, 133ms, 160ms) und somatosensibel evozierter Potentiale (VEP) als Doppel- und Einzelreize. Die Berechnung der Kohärenzen erfolgte aus Elektrodenpaaren im Bereich der Frequenzen 8-12, 13-29 und 30-60 Hz. Nur im visuellen System zeigte sich eine Veränderung der Doppelreiz-VEP für die SOA 107 (p=0,006) und 133ms (p=0,007) sowie der Kohärenz bei 8-12 Hz (p=0,03) und somit eine gesteigerte Exzitabilität und Konnektivität. Es werden weitere Studien benötigt um die durch Noradrenalin modulierte Exzitabilität bei Lernprozessen oder im Rahmen der Rehabilitation zu untersuchen

Sesquiterpenes of the Geosmin-producing cyanobacterium Calothrix PCC 7507 and their toxicity to invertebrates

The occurrence of sesquiterpenes was investigated with the geosmin-producing cyanobacterium Calothrix PCC 7507. The essential oil obtained by vacuum destillation was studied in more detail by GC-MS methods and superposition with authentic compounds. Geosmin was the dominating compound while the other sesquiterpenes were minor components. Sesquiterpenes that have not been described before in cyanobacteria were isodihydroagarofuran, eremophilone and 6,11-epoxyisodaucane. Closed-loop stripping analysis revealed that most of the sesquiterpenes were found in the biomass of Calothrix, while eremophilone was mainly observed in the medium of the axenic culture. Eremophilone showed acute toxicity (LC(50)) against Chironomus riparius (insecta) at 29 mu M and against Thamnocephalus platyurus (crustacea) at 22 mu M. The compound was not toxic for Plectus cirratus (nematoda). 6,11-Epoxyisodaucane and isodihydroagarofuran exhibited no toxicity to invertebrates when applied ill concentrations up to 100 mu M